Failure of anticancer drug treatment is largely due to overexpression of the P-gp/BCRP drug efflux system at the blood-brain barrier. New evidence suggests that glioblastoma multiforme (GBM) induces P-gp/BCRP over- expression in capillaries of the brain hemisphere that is contralateral to the tumor. Thus, after surgical removal of the primary tumor, remnant tumor cells that are scattered throughout the brain remain shielded from anti- cancer drugs. This poses a significant clinical problem and represents an unmet critical need to develop strat- egies to overcome P-gp/BCRP. The absence of such strategies will likely prevent improvements in GBM ther- apy. The long-term goal of the investigator is to identify molecular mechanisms that control blood-brain barrier function and can be targeted to improve brain uptake of anticancer drugs. The overall objective of this applica- tion is to develop an effective therapeutic strategy to overcome P-gp/BCRP-mediated anticancer drug efflux and prolong survival in mice with GBM. Based on preliminary data the central hypothesis is that GBM induces P-gp/BCRP overexpression and that inhibiting PI3K/Akt will decrease P-gp/BCRP overexpression, which will increase brain uptake of anticancer drugs, thereby reducing tumor size and prolonging GBM mouse survival. The rationale for this research is that its successful completion is expected to provide a solid, evidence-based scientific framework for translating our strategy into the clinic. Based on strong preliminary data, this hypothesis will be tested by pursuing three specific aims: 1) Determine the mechanism(s) by which GBM induces P-gp/BCRP overexpression; 2) Identify pathways that regulate P-gp/BCRP at the human blood-brain barrier; and 3) Develop a therapeutic strategy to increase anticancer drug brain uptake in GBM mice. Under the first aim, mechanistic steps involved in GBM-induced overexpression of P-gp/BCRP will be assessed in brain capil- laries of the hemisphere contralateral to the primary tumor. The impact of blocking these steps on brain uptake of anticancer drugs in GBM-bearing mice will be determined. Under the second aim, P-gp/BCRP regulation by the PTEN/PI3K/Akt/mTOR pathway will be determined in brain capillaries from normal individuals and from GBM patients. Under the third aim, the therapeutic benefit of combining PI3K/Akt inhibitors with anticancer drugs to reduce P-gp/BCRP levels with the goal of improving brain uptake of anticancer drugs and prolonging survival will be assessed in three different GBM models. The proposed research is innovative, in the appli- cant's opinion, because it represents a new and substantive departure from the status quo by shifting the focus to GBM-induced overexpression of blood-brain barrier P-gp/BCRP in the contralateral hemisphere and by uti- lizing a molecular switch-based approach to overcome P-gp/BCRP-mediated drug efflux to target remnant tu- mor cells distant from the primary tumor. The proposed research is significant because it is expected that the new knowledge may have broad translational importance in the treatment of patients with GBM and potentially other brain tumors as well.